1. Field of the Invention
The present invention relates to a thin film magnetic head constructed for two-channel tracking, more particularly,to a thin film magnetic head which is capable of adjusting equalization between the outputs of the two channels.
2. Description of the Prior Art
According to the prior art, a thin film magnetic head is covered by a firm adhesive layer, a protective holding plate, or the like, because of the mechanical weakness of the thin film layer. Due to this, the magnetic gap in the magnetic head is opaque from the outside, making it difficult to adjust precisely the depth of the magnetic gap (gap depth) at the time of manufacturing the magnetic head. For this reason, thin film magnetic heads with the construction in which a plurality of gap depth detection marks are installed on both sides of the magnetic core of the magnetic head for adjusting the gap depth have been known in the past. A thin film magnetic head of this type has been disclosed in Japanese Patent Publication for Opposition No. 52-38402.
Now, in making a two-channel thin film magnetic head to be used for a two-channel head recording device for revolving memory sheets(for example, a device in which frame memories are obtained by recording one field on each of the adjacent tracks), it was necessary to obtain equal output characteristic between the channels. Therefore the gap depths of the bead sections of both channels are made so as to have an indential size.
Moreover, in order to realize satisfactory interfacing the head with the revolving magnetic sheet, it is desirable to choose the form of the head surface opposite to the magnetic sheet to be roundish with the gap section as the crest, and also to give gentle curvatures to both sides of the head surface in the direction of the track width. Therefore, it is difficult to install depth detection marks on both sides of the head sections of the two channels in the manner like in the prior art construction. That is, in forming curved surfaces on both sides of the head, it is impossible to realize precisely the radii of curvature that are defined delicately, and hence it is difficult to preset the positions of the detection marks.
For the reasons described in the above, new gap adjusting means particularly for the two-channel thin film magnetic head has been required.